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Laser lithotripsy

- Jun 27, 2018 -

The laser appeared in 1960. In 1968, Mulvaney first used a ruby laser to crush the stones. Due to too much heat, it caused severe tissue damage and was quickly abandoned. Later, the use of continuous wave laser lithotripsy, CO2 laser, doped ytterbium: yttrium aluminum garnet laser (Nd: YAG) and so on. CO2 laser can effectively gravel in the air, but the energy decays rapidly in water. When gravel is broken, gas must be injected into the body. It is difficult to apply in clinical practice. Although Nd:YAG laser can effectively gravel in water, but the required energy is very high, in addition to causing serious tissue thermal damage, but also very easy to damage the optical fiber. Therefore, this kind of laser is gradually being eliminated. The above lasers are all made by direct action of the laser. In the 1980s, pulsed lasers replaced continuous-wave lasers. The former can convert the laser energy into shock waves, so the heating effect is significantly reduced. Clinical applications have demonstrated that such lasers have high litholytic efficiency and a relatively low incidence of complications. Currently used gravel lasers are Q-switched Nd:YAG (Q-Nd:YAG), dye laser (dyelaser, DL), alexandrite laser (AL), Y:YAG laser (Holmium:YAG, Ho:YAG) etc.

Like EHL, the gravel effect of all LLs currently depends on the generation of plasma and shock waves. The difference is that EHL is generated by the discharge, and the laser is formed by photodecomposition. After receiving high-energy, high-density laser radiation, the stone rapidly forms a plasma on its surface, which in turn generates shock waves and micro-jets that crush the stones. Different pulse width lasers produce different shock waves. The Q-Nd:YAG with the shortest pulse width mainly depends on the expansion of the plasma to form the shock wave, while the rest of the three lasers, the collapse of the cavitation bubble, are the main reason for the generation of the shock wave

4.1Q-Nd:YAG

</strong>The principle of laser Q-switching is that the Q value of the optical resonator changes rapidly with a Q-switch, which results in a very short pulse (ns level) and a very high peak power (a few million watts). Shockwave, which is the conversion of continuous wave lasers to pulsed lasers. In 1983 Watson first used the Q-Nd:YAG laser lithotripsy, which worked well, but at the time the glass optical fiber could not withstand the high energy required for the gravel. In 1989, Hofmann switched to quartz optical fiber and achieved a complete stone breakage rate of 90%. No thermal damage to the tissue occurred. The optical fiber was intact, but it was impossible to break the calcium oxalate monohydrate stone.

4.2DL

</strong>This is a pulsed tunable laser designed specifically for crushed stone and was first used clinically by Drelter et al. in 1987. DL uses the liquid coumarin green dye as the excitation medium. Adjusting the dye can change its wavelength. The laser energy can be absorbed by most of the stones, but it is not absorbed by water. The ureter can absorb less but can be reflected. Therefore, most of the stones can be effectively broken without damaging the ureter. Calcium oxalate monohydrate does not work well. Because cystine stones reflect a large amount of laser light, it is difficult to form a plasma on the stone surface, and the effect of gravel is also poor. In this regard, Tasca (1993) used rifampicin-encapsulated stones (a 2% rifampicin solution as a perfusion solution) to enhance the laser absorptivity of cystine stones and improve lithotripsy efficiency. Of course, this method can also be used for other laser lithotripsy.

4.3AL

</strong>Unlike other lasers, the excitation medium for AL is solid. Like the pulse DL, this laser has a shorter pulse width. The physical characteristics and gravel mechanism of the two are basically the same, and can be absorbed by most of the stones, resulting in strong plasma effects and shock waves. The difference is that AL can break hard stones such as cystine stones and calcium oxalate monohydrate stones. The calcium oxalate dihydrate effect is poor.